1. Field of the Invention
This invention relates to a photo-mask that is used in the manufacture of optical memory devices with which information can be optically recorded, reproduced and erased.
2. Description of the Prior Art
A conventional photo-mask is composed of, as shown in FIG. 6, a light-permeable substrate 11 and patterned metal films 12 of Ta, Cr, Ti or the like that are buried in the substrate 11. Another conventional photo-mask is composed of, as shown in FIG. 7, a light-permeable substrate 11 and patterned metal films 12 that are disposed on the top surface of the substrate 11. When guide grooves with a width of 0.6-1.3 .mu.m are formed on a glass substrate that constitutes an optical memory device by the use of the photo-mask, the photo-mask must be brought into contact with a photo-resist that has been disposed on the glass substrate, so that the mask-pattern of the metal films 12 can be transferred onto the photo-resist.
When the transference of the photo-mask onto the photo-resist is conducted, the photo-mask is stained because a piece of the photo-resist sticks to the photo-mask and/or dust enters into a gap between the photo-resist and the photo-mask. To remove the stain from the photo-mask, the photo-mask is subjected to an ultrasonic washing treatment, which causes peeling-off of the metal films 12, resulting in a loss of the mask-pattern of the metal films 12. Moreover, when the photo-mask shown in FIG. 6 is brought into contact with a photo-resist that has been formed on the glass substrate of an optical memory device, static electricity occurs and is accumulated in the light-permeable substrate 11 that is non-conductive, which causes damage in the metal films 12.